1. Field of the Invention
The present invention relates to a medical device having a main tube which has a branch (e.g. Y and T tubes) connected to a branchline tube (for injecting medical fluids into the main tube and for monitoring the pressure on the main tube). The invention also relates to a medical device which has a plug fitted into the branch to form processing portions for performing several functions such as injection of medical fluids into the main tube (in this case, the processing portion is a mixing/injecting portion), sampling fluids from within the main tube (a fluid sampling portion) and monitoring the pressure in the main tube (a pressure monitoring portion), as exemplified by body fluid processing circuits, administration, blood sampling and blood transfusion sets, as well as administration, blood sampling and blood transfusion bags which are to be used either alone or in connection to those sets and circuits. The invention also relates to a process for producing such medical devices.
2. Description of the Related Art
The present invention will now be described in detail with particular reference to a body fluid processing circuit including a main tube made of a synthetic resin and which has branchline tubes and processing portions such as a mixing/injecting portion welded at several sites along its length, as well as to a process for producing the circuit.
As is well known, artificial kidneys, artificial lungs, plasma separators and other body fluid processors are equipped with body fluid processing circuits for connecting these apparatus to the human body. FIG. 36 shows an exemplary arterial blood circuit to be connected to an artificial kidney. As shown, the circuit includes a main tube 101 which usually has many branches provided along its length and they include a physiological saline filling line 102, a mixing/injecting portion 103 and a heparin line 104. Conventionally, the production of such branches has involved very cumbersome steps and required considerable skill.
A section of the mixing/injecting portion 103 is shown in FIG. 37. The conventional procedure of assembling this portion is shown in FIG. 38 and includes cutting the main tube 101 at a suitable site, applying a solvent 105 to the tips of the cut sections of the tube 101, pressing them into a connecting tube 107 with fingers, subsequently inserting a rubber plug 108 such as to close an opening 106 in the connecting tube 107 and fitting a cover 109 over the rubber plug 108.
This procedure is entirely manual and hence very cumbersome; in addition, controlling the coating weight of the solvent is difficult and requires considerable skill. If the solvent is applied in a more-than-necessary amount, the excess portion will come out of the joint, protrudes inward of the tube and solidifies to form lumps indicated by 110 in FIG. 37. The lumps 110 will increase the frictional resistance of blood flowing through the main tube, causing a turbulence in the blood which should form a laminar flow in a normal smooth conduit. This can be a cause of the disruption of blood components, which in turn may induce blood coagulation.
If the amount of the solvent is unduly small, not only is the main tube 101 joined to the connecting tube 107 insufficiently but also the resulting gap may potentially provide a passageway for the leakage of blood. In addition, the method of joining the two members by solvent application has a microbial contamination hazard or the solvent may dissolve in the blood to potentially cause adverse effects on the human body.
The following disadvantages and defects have been additionally pointed out to exist in the related art: (1) while the main tube 101 is molded by extrusion, the connecting tube 107 must separately be formed by injection and due to the different shrinkage ratios of the two molded parts, they cannot be joined together without producing steps in the joint; in addition, so many parts have to be assembled that the production cost increases and parts control is prone to be a cumbersome task; (2) the bore of the main tube 101 has to be adjusted to the exact dimension which fits to the connecting tube 107 and, in addition, it must be cut to the specified correct length; this only adds to the number of production steps and, hence, the manpower that is required; (3) due to the distortion introduced in the cut surfaces of the main tube 101, the latter will not fit closely to the connecting tube 107 and the applied solvent will adhere firmly to unwanted areas, thereby forming asperities which in turn cause blood coagulation and other troubles; (4) post-assembly sterilization will distort the joint between the main tube 101 and the connecting tube 107 and the distorted areas become accordingly smaller in diameter or steps may form to thereby upset the blood flow, which can be a cause of blood coagulation, residual blood or hemolysis.
For example, even a step about 0.1 mm (100 .mu.m) high which is difficult to identify with the naked eye is an obstacle at least 10 times as large as erythrocytes which are the largest (8 .mu.m is diameter) of the blood components; see FIG. 39 which shows enlarged encircled area A of FIG. 37. As a result, erythrocytes in the blood flowing through the main tube 101 to enter the connecting tube 107 impinge on the step and cannot move any farther. The erythrocytes gradually build up in areas around the step to become a cause of blood coagulation or residual blood and the disrupted erythrocytes resulting from the impingement will be a cause of hemolysis.
(5) The opening 106 in the connecting tube 107 is also wide enough to potentially cause the same problem as described in (4), i.e., blood may build up in areas about the step of the opening 106 to thereby cause clotting and residual blood.
(6) In the structure shown in FIG. 37 which has the main tube 101 connected to the connecting tube 107, the former is typically formed of a flexible synthetic resin and the latter of a rigid synthetic resin; hence, as shown in FIG. 40, the main tube 101 often kinks at sites near the connecting tube 107.
Under the circumstances, Japanese Patent Unexamined Publication No. 124249/1995 discloses a body fluid processing circuit having a main tube formed to have a straight surface without any seams present along its length, as well as a process for producing the circuit.
However, because of the absence of any holes in the main tube at the site where the mixing/injecting portion is formed, it is difficult to pierce a needle into the main tube. On the other hand, a small hole 121 (see FIG. 41) is formed in the mounting surface of the main tube 124; however, as is clear from FIG. 41, the small hole is formed with its outer peripheral surface protruding inward and when blood or other medical fluids contact the protrusion 122, there is the possibility for the occurrence of stagnation, clotting, residual blood and other troubles.